Histopathological changes induced by ergasilid copepod infections on the gills of food fish from Batticaloa lagoon, Sri Lanka
Histopathological changes induced by ergasilid parasitic infections on the gills of economically important fish from Batticaloa lagoon were investigated from October 2003 to November 2004. Anabas sp, Ambassis gymnocephalus, Chanos chanos, Cirrhinus mrigala, Etroplus suratensis, E. maculatus, Hemirhamphus sp, Leiognathus splendens, Lutjanus sp, Mugil cephalus, Nematalosa nasus, Oreochromis mossambicus, Siganus lineatus, S. oramin, Tachysurus sp, Terapon jarbua and Triacanthus brevirostris were naturally infected with the ergasilids viz. Ergasilus sieboldi, E. parvitergum, and Dermoergasilus sp. Intensity of infection ranged from 0 to 30 ergasilids per host fish. Histopathological investigations of infected gills showed extensive tissue damage due to attachment and feeding of ergaslids. Ergasilus sp attached close to the base of the filaments near the gill arch and the pressure exerted by the parasite attached to the lateral margin of the gill filaments induced atrophy of the secondary lamellae. Tissue reactions included hyperplasia and mucous cell proliferation of the gill epithelium and damaged primary and secondary lamellae. In addition, considerably high numbers of eosinophilic granular cells and rodlet cells were noticed in the gills of the infected fish. Histopathological changes induced by the ergasilid infections would adversely affect the proper functioning of the gills of these host fish. Mass mortalities of the fish inhabiting Batticaloa lagoon which occurred during April and May 2004 may be attributed to the infection of the fish gills by these ergasilids.